This research investigates the daily emotional states of young adolescents in order to shed light on the often discussed, but inadequately studied, issue of adolescent "storm and stress." The first objective is to determine whether emotional variability during this period is associated with potential biological, social, and/or cognitive sources of stress or disruption. The second aim is to determine whether this variability is in turn related with mental health and illness. A stratified random sample of 400 fifth to eight graders will be studied. Following procedures of the Experience Sampling Method (ESM), these subjects will provide self-reports at random times during a week in response to an electronic pager. The reports will obtain information on emotional states, activities, and perceived stressful events at each moment in time. Every subject will fill out 40 to 50 such reports; hence the study will produce a file of information on close to 20,000 random moments of young adolescents' daily experience. Questionnaire and interview data also will be obtained from the subjects and their parents. Multiple measures of pubertal status and the social, cognitive, and adjustment variables will be obtained from questionnaires and interviews with both the child and a parent, from the school records, and from teachers. The focus of analyses will be on the experience of stress in daily life, defined in terms of the students' reported average emotional states and the variability of these states. After appropriate stages of data reduction, LISREL will first be used to evaluate the relation of the subjects' emotional states with their pubertal status, their social and familial life situation, and their level of cognitive reasoning. Second, a similar procedure will be used to assess the relationship of daily emotional states to assessments of psychological disturbance.